Design Code in Multiple Files

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​Compilation Process

Starting with source code (e.g. C++) and converting it into machine code that the computer can run.

The process

Actual Process

Separate Declaration from Definition

// functions.h
#ifndef FUNCTIONS_H
#define FUNCTIONS_H
int gcd(int, int);
int factorial(int);
int mod_pow(int, int, int);
#endif

// functions.cpp
#include “functions.h”
int gcd(int a, int b) {…}
int factorial(int n) {…}
…

Group Related Functions Together

// math functions
#ifndef MATH_H
#define MATH_H
…
double exp(double);
double log(double);
double pow(double, double);
double sqrt(double);
…
#endif

// string functions
#ifndef STRING_H
#define STRING_H
…
int find(string, string);
int length(string);
string lower(string);
string upper(string);
string reverse(string);
…
#endif

Header Guards

#ifndef NAME_OF_FILE_H
#define NAME_OF_FILE_H
…
#endif

• Prevents double inclusion: inclusion of same header file multiple times

  • Helps prevent linker error due to multiple definitions (re-definition)

• #ifndef

  • pre-processor directive “if not defined"

Including and Compiling

// source1.cpp
#include <c++_library>
#include <c_library.h>
#include
“user_defined_library.h”
…

// source2.cpp
#include
<iostream>
…
int main() {…}

//$ g++ source1.cpp source2.cpp source3.cpp